1. Technical Field
This invention relates to an amplification control scheme for a receiver used in wireless communications.
2. Related Art
A wireless communication system uses transmitters, receivers or transceivers to facilitate the exchange of data between electronic devices. In an open specification environment, the data structure of data packets is often described in technical specifications related to the open standard to promote the wireless operability between different electronic devices. For example, the Bluetooth standard may allow products from different manufacturers to communicate and understand each other over a short distance.
A wireless communications protocol, such as that defined by the Bluetooth standard, may include a data structure of a data packet. For example, a data packet may comprise a preamble (e.g., an access code preamble) at or near a beginning of a data packet. The data of a preamble may be subject to corruption where a low-noise amplifier is switched into and out of the received signal path to adjust the amplification of the received signal. The low-noise amplifier may be switched into and out of the received signal path to maintain an appropriate signal strength range above the noise floor. If the data of the preamble is corrupted, the function or data processing supported by the data of the preamble may be lost or degraded. In one example, a preamble of the data packet may contain data that facilitates reduction of a direct current component introduced by any frequency offset of the receiver with respect to the transmitted signal. In another example, a preamble of a data packet may contain synchronization data to synchronize the modulator of a transmitter and the demodulator of a receiver. Accordingly, corruption of the preamble may degrade the modulation performance because of the presence of an increased, direct current component in the received signal, deficient or inaccurate synchronization information, or both. Thus, a need exists for an amplification control scheme for a receiver to support reliable operation of the demodulator of the receiver, while maintaining an appropriate signal strength range.
An amplification control scheme of a receiver is provided and may be performed in the digital domain to support the switching of an amplifier or the adjustment of gain of the amplifier with respect to a received signal path in a manner that preserves the integrity of data or a payload within at least one data packet. The amplification control scheme may be well suited for enhancing the demodulation performance of the receiver over a broad dynamic range of received signal strengths.
A frequency offset estimator reads a group of bits or symbols at or near the end of an access code of a data packet to enhance demodulation performance. For example, the group of bits may be trailing bits extracted from a trailer of an access code of the data packet or, in the absence of a trailer, data bits extracted from a group of bits in a Baker sequence. An unwanted direct current component may be attributable to a possible difference between the local oscillator frequency of the receiver and the oscillator frequency of the transmitter or any propagational anomalies introduced in the propagation path between the transmitter and receiver. The frequency offset estimator may determine a compensatory frequency offset in the digital domain to compensate for drift or any other difference in the frequency of oscillation of the transmitter and receiver communicating therewith. The reduction or elimination of frequency offset in the digital domain may be achieved by manipulating (e.g., adding) a compensatory direct current component with respect to the digital baseband signal to compensate for the unwanted direct current component. The compensatory direct current component may have a magnitude opposite to that of the unwanted direct current component, where the compensatory direct current component is added to the digital baseband signal to reduce or eliminate the unwanted direct current component.
A matched filter or a timing estimator may perform correlation between a received signal and a reference signal to detect a burst of a data packet of the received signal and to determine the timing parameters associated with the burst. In one embodiment, the timing estimator may include a correlator for determining the correlation between a receive set of bits in a receive data packet and a reference set of bits in a reference data packet (e.g., synchronization word). The received set of bits and the reference set of bits generally coincide in logic value (or are at least highly correlated) when synchronization or temporal alignment is achieved between the received signal and locally generated signals. The modulator of the receiver is synchronized with the modulator of the transmitter by delaying or otherwise filtering the received signal consistent with the detection of the general peak of the correlation.
Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.